The symptoms of allergy in humans and animals are primarily attributable to the release of histamine and a large variety of other bioactive compounds from mast cells and related cell types. The mast cell contains numerous secretary granules in which these substances are stored at extremely high concentrations. Activation of the mast cell results in the fusion of these granules with the cell surface membrane, leading to the exocytosis of the granule contents and the concomitant induction of allergic symptoms. The plasma membrane of these cells are endowed with receptors for the Fc portion of the IgE (Fc.epsilon.RI). This receptor binds circulating IgE with very high affinity and retains it at the mast cell surface for extended periods of time. Activation is accomplished through the binding of an allergen simultaneously to more than one polyvalent molecule of Fc.epsilon.RI-bound IgE. This "cross linking" of at least two surface-bound IgE molecules brings Fc.epsilon.RI proteins into close association with one another in the plane of the mast cell plasma membrane. Kinases associated with these receptors become activated as a result of this proximity, initiating the second messenger cascade which results in cell degranulation.
At least one other class of receptors can bind to the Fc portion of IgE. The low affinity receptor for IgE, Fc.epsilon.RII (also known as CD23) is expressed on mast cells and related cell types, B cells, and subsets of antigen presenting cells. It has been suggested that occupancy of Fc.epsilon.RII negatively regulates IgE synthesis.
It is an object of the present invention to provide a means and method of preventing activation and degranulation of mast cells and related cell types in response to exposure to allergens.